Process and device for preheating pulverulent material



Jan. 28, 1964 w. BERZ 3,119,605

PROCESS AND DEVICE FOR PREHEATING PULVERULENT MATERIAL Filed June 30,1961 2 Sheets-Sheet 1 w. BERZ 3,119,605

PROCESS AND DEVICE FOR PREHEATING PULVERULENT MATERIAL Jan. 28, 1964 2Sheets-Sheet 2 Filed June 30, 1961 FIG.2

United States Pate My present invention relates to a process and adevice for-preheating pulverulent material adapted to be introduced intoa furnace or the like. This application is a 'continuation-in-part of myco-pending-application Ser. No.- 549,122, filed November 25, 1 955, andnow abandoned.

An object of 'the' invention resides in the provision of an improvedpreheatingdevice for-pulverulent materials adaptedto afford highlyeflicient transfer of heat from a hot gas to the particularizedmaterial;

Another object of my invention is to provide-an-effi cient process formaintaining a mass of free-flowing solid particles in prolongedcontact'with a stream of heating gas therefor. H.

-Afurther object of this inventionis to provide a device forpreheatingcomminuted material, morespecifically dry; rawcement free from anybinder and adapted to.be fed continuously into conventional kiln, withefiicient utilization of the heat content of furnace orwkiln exhaustgases.---.

According to a featureof my invention, a preheating device for'pulverulent materialscomprises a preheating chamber formed with atleast.one apertured collecting plate or partition disposed transverselyto a descending stream of particles and an ascending flow of furnace orkiln exhaust gas, the collecting plate being formed withpassagesadaptedto admit the exhaust gas to the upper compartment of the chambersubstantially tangentially,

thereby sweeping the comminuted material falling onto the plate into avortex and maintaining it in contact with.

the gas stream for prolonged periods. Gradually and continuously,however, these particles traverse the passages in the plate and enterthe lower compartment of thechamber whence they may be conveyed to themain heating or firing furnace. The preheating chamber may,advantageously, be provided with two or more stages formed byasuccession of spaced-apart collecting plates, thereby increasing theefiiciency of the device still further. According to a more specificfeature of the invention, the cyclonic effect of thetangential passagesin each collecting plate is enhanced by the provision of means on theupper surface of the plate-for subdividing the vortex in the'uppercompartment into a pluralityof concentric cyclonic'whirls. Such meansmay includea ridge lo cated between two concentric annular arrays of theaforementioned passages and forming a pair of downwardly convergingannular troughs which open into the upper compartment and are adapted tofunnel the descending stream of particles toward the passages Whiledirecting the vortex upwardly so as to spread the stream of circulatingparticles over substantially the entire region above the plate. aMoreover, as mentioned in the above-identified copending application, Ihave found that it is advisable to control the quantity of particlespermitted to pass through the passages in accordance with the quantityof pulverulent material present above a collecting plate; in thismanner, given a predetermined supply rate for this material, the averagelength of exposure of the particles to the hot gas can be-adjusted to anoptimum value. I have further found that it is possible to stabilize thetreatment time by measuring the pressure differential between thecompartments respectively formed above and below the partitioning plate.Although a portion of this differential arises as a consequence of apressure drop as the rising stream'of exhaust gas traverses the passagesin the plate, the major portion of the pressure differential 'ap-,

pears to result from a pressure drop as the gas passes through theswirling cloud of comminuted material floating above the plate.Ltherefore, prefer to providemeans responsive to a pressure differentialon opposite sides of a collecting plate for controlling the openings'ofthe passages in this plate. Suitable meansof this type may comprise anapertured valve member juxtaposed with; the collecting plate, the-valvemember and the collecting plate being relatively angularly shiftable forselectively Ili1ll of FIG. 2, still further enlarged; and

obstructing the passages therein to a varying extent with-- out,however, closing them completely in the normal operation of the device,I In'a general manner, the width of the passages is made to vary instepwith the pressure differential so that any change in the thickness ofthe float-- ing layer is compensated by an altered rate of descent oftheparticles through these passages.

"I0 obviate ;the formation of channels within the pulverulent material,I prefer to provide agitator means adapted to sweep the collectingplates. Such agitator meansmay comprisea radially extending arm disposeda limited distance above the upper surfaces of each 'col-.

lecting' plateandrot'ated continuously. When the device is a-multi-stagepreheater, theagitating arms of several collectingplates are,preferably, ganged for rotationin unison by a single drive. I I v 7While the exhaust gas may be introduced into the preheating chamberunder a pressure sufficient to drive it through the passages of thecollecting plates, I prefer to provide a reduced-pressure'chamber abovethe preheatingchamber for drawing'the exhaust gas'upwardly. Thereduced-pressure chamber may advantageously, cornprise a precipitatoradapted to collect dust andv the like carried along with the gas andconnected in series with a suction-device. Suitable feed m eans may beprovided for returning the comminuted material accumulated by. theprecipitation device to the main heating furnace, either directly or viaone or more-of the associated preheating stages. I

' The above and other. objects, features and advantages of my presentinvention will become more readily appar-. ent from the followingdescription, reference being made to'the accompanying drawing in which:f

' FIG. 1 is a cross-sectionalview of a preheating device, illustratedsomewhat schematically, according to the invention; I f 7 FIG. 2-is across-sectional view taken along line II.-II of FIG. 1, drawn to anenlarged scale; 7

.- FIG. 3 is a cross-sectional View taken along line FIG. 4 is across-sectional view taken along line IV-IV of FIG. 1 and drawnto thesame scale as FIG. 2.

' In the drawing, a conventional rotary kiln 10 for firing cement or thelike, iournaled on rollers 11, is connected via a duct 12' to acylindrical casing 13 which encloses a preheating chamber 14. The latteris subdivided into an upper compartment 15, an intermediate compartment16 and a lower compartment 17 by a pair of axially spaced. collectingplates 18 and 19 forming horizontal partitions therein. A feed hopper2i) and a feed roller 21, adapted to admita continuous stream of'comminuted material 2am a housing23 communicating with the uppercompartment .15 of the chamber 14, are mounted nponithe top of thishousing. The latter also enclosesa precipitating cone 2.4 which isconnected to a suction pumpQSby .a conduit26 and has a seriesof'periphera'l inlet ports 27 The dust and fine particles entrained bythe. gases emerging from the preheater are separated therefrom bydeflection of the fiowwithin cone 24 and are returned to v the kiln 10via a screw feed 28' and a duct 29 represented diagrammatically bydot-dash lines.'

Patented Jan. 28, 1964 The collecting plate 19, shown in greater detailin FIGS. 2 and 3, is formed with two concentric annular arrays ofarcuate throughgoing slots 30 and 31 provided with respective deflectingvanes 32, 33 forming helicoidally ascending ramps therein. As shown inFIGS. 2 and 3, the vanes 32 and 33 are inclined upwardly in thecounter-clockwise direction and adapted to impart a tangential directionto the ascending gas stream symbolized by arrows 34 in FIG. 1. The plate19 is also provided with an upstanding central conical portion 35, anouter conical wall 36 and a ridge 37 with conical wall portionsintermediate the slots 30 and 31. The cone 35, the wall 36 and the ridge37 form a pair of concentric troughs 38, 39, respectively communicatingwith the slots 30, 31, of downwardly converging configuration andadapted to funnel the descending particles 22a to the slots, at the sametime sustaining independent vortices arising from the tangential flow ofascending gas which issues from the passages constituted by the vanes32, 33 and the slots 30, 31. A valve disk 40 abuts the lower surface ofplate 19 and is rotatable upon a ring 41 secured to the casing 13. Asolenoid 42 has its armature 43 pivoted to the disk 40 along itsperiphery and is adapted to displace it relatively to the plate 19whereby the bores 44 in the disk will be angularly displaced out ofalignment with the passages 30 and 31 and the quantity of pulverulentmaterial traversing the latter will be propressively reduced.

The upper collecting plate 18 (FIGS. 1 and 4) consists of a centralmember 45 and an outer member 46 each formed with a respective array ofangularly spaced slots 48, 47. The slots are provided with deflectingvanes 50, 51 of the type described above for imparting a tangentialcomponent to the ascending flow of gas. Each of the members 45, 46 isarticulated to a connecting rod 52, 53, respectively joining them to thearmatures 54, 55 of a pair of solenoids 56, 57, and is rotatablerelatively to a stationary valve disk 58 whose bores 59 are alignablewith the slots 47 and 48 as described with respect to the movable valveplate 40.

A pair of agitator blades 60, 61, adapted to sweep the upper surfaces ofplates 18 and 19, respectively, and to prevent the formation of ductsfor the gas stream through the overlying mass of comminuted materialwhich would then tend to settle upon the plates, are each secured to ashaft 62 journaled axially in the chamber 14. Shaft 62 is driven via abevel-gear linkage 63 by a motor 64. The speed of shaft 62 is, ofcourse, such that the blades 60, 61 rotate at a rate different from theangular velocity of the swirling gas stream.

In operation, the comminuted material 22 is percolated downwardly fromthe hopper 20 and the feed roller 21 through the preheating chamber 14in countercurrent to an ascending stream of hot exhaust gas (indicatedby the arrows 34) aspirated from the rotary kiln by the suction pump 25.As the gas rises through each plate 18, 19, the passages therein impartto the velocity of the gas a tangential component which entrains thedescending particles in rising vortices above each plate so that theparticles are floated for prolonged periods (e.g. of about to 40minutes) and abstract a maximum amount of heat from the gas. Thedepleted gas then flows through the precipitator '24 for the recovery ofaccompanying solids and is discharged via pump 25.

To control the rate at which particles are fed to the kiln and tosuccessively lower plates in the preheating chamber and to maintain thelayers of particles above these plates 18 and 19 at a substantiallyconstant thickness, a respective pressure cell 65, 66 and 67 is disposedin each compartment 15, 16 and 17. The cells 65, 66 are connected acrossa pressure-difierential-responsive switch 68 lying in series with abattery 69, representative of any convenient source of electric current,and the parallelconnected solenoids 56 and 57. A cutout switch 70 inseries with the solenoid 57 serves to disconnect this solenoid from thedifferential switch 68 if the operation of solenoid 56 is sufiicient tocontrol the flow of particles through the plate 18. Similarly, solenoid42 is con nected in circuit with a battery 72 and a differential switch71. The latter bridges the pressure-sensitive cells 66 and 67. Thisconstruction permits the rate of particle flow through each plate to beadjusted in keeping with the depth of the particle layers suspendedthereabove.

The invention as described and illustrated is believed to admit of manymodificaions and variations embraced within the spirit and scope of theinvention as claimed and readily apparent to persons skilled in the art.Thus, for example, the eflective cross-sectional area of passages 30, 31and/or 47, 48 might be controlled in response to parameters other thanthe pressure differential across the particle layer overlying therespective collecting plates, for the purpose of establishing a desiredlayer thickness along with an optimum floating time; also, the severalpreheating stages may all be provided with collector assemblies of thetype shown either at 18 or at 19, with or without agitators, havingtheir vortex zones arranged in a variety of geometric patterns.

I claim:

1. A device for heating pulverulent material, comprising a housingforming a heating chamber, duct means for introducing a flow of hot gasinto a lower portion of said chamber, feed means for introducing astream of pulverulent material into an upper portion of said chamber incounterfiow to said hot gas, a perforated collecting plate positionedintermediate said upper and lower portions for intercepting said streamof pulverulent material and said flow of hot gas, and valve meansresponsive to a pressure differential in said chamber on opposite sidesof said plate for maintaining the thickness of a layer of said materialdeposited thereon near a predetermined value.

2. A device for heating pulverulent material, comprising a housingforming a heating chamber, duct means for introducing a flow of hot gasinto a lower portion of said chamber, feed means for introducing astream of pulverulent material into an upper portion of said chamber incounterflow to said hot gas, a perforated collecting plate positionedintermediate said upper and lower portions for intercetping said streamof pulverulent material and said flow of hot gas, said collecting platebeing formed with a plurality of passages for imparting a substantiallytangential displacement to the gas passing through said plate into saidupper portion whereby particles of said material are entrained in avortex of said gas rising from said plate, and valve means responsive toa pressure difierential in said chamber on opposite sides of said platefor maintaining the thickness of a layer of said material depositedthereon near a predetermined value.

3. In combination with a furnace, a device for preheating pulverulentmaterial, said device comprising a housing forming a heating chamber,duct means connected to said furnace for introducing a flow of hotexhaust gas into a lower portion of said chamber, feed means forintroducing a stream of pulverulent material into an upper portion ofsaid chamber in counterflow to said hot exhaust gas, a pair oflongitudinally spaced perforated collecting plates extendingsubstantially horizontally intermediate said upper and lower portionsfor intercepting said stream of pulverulent material and said flow ofhot gas, said collecting plates being formed with a plurality ofpassages for imparting a substantially tangential displacement to thegas passing through said plate into said upper portion whereby particlesof said material are entrained in a vortex of said gas rising from saidplate, valve means responsive to a pressure differential in said chamberon opposite sides of said plate for maintaining the thickness of a layerof said material deposited thereon near a predetermined value, and meansfor separating particles of said material from the gas flow passed bysaid late and returning them to said furnace.

4. In a device for heating pulverulent material, in combination, ahousing, substantially horizontal partition means in said housingsubdividing the interior thereof into a lower and an upper compartment,said partition means being formed with at least one passageinterconnecting said compartments, a source of pressure differentialbetween said compartments, means including said source for passing aflow of hot gas upwardly through said passage from said lower to saidupper compartment, adjustable valve means in said passage, feed meansfor continuously introducing a supply of said pulverulent material intosaid upper compartment in counterflow to said gas, andgas-pressure-responsive control means sensitive to the pressurediiferential between said compartments and coupled with said valve meansfor maintaining the rate of gas how at a value adapted to hold saidpulverulent material fioatingly suspended above said partition means foran extended period.

5. In a device for heating pulverulent material, in combination, ahousing, substantially horizontal partition means in said housingsubdividing the interior thereof into a lower and an upper compartment,said partition means being formed with an array of helicoidallyascending passages interconnecting said compartments, a source ofpressure differential between said compartments, means including saidsource for passing a flow of hot gas upwardly through said passages fromsaid lower to said upper compartment, adjustable valve means in saidpassages, feed means for continuously introducing a supply of saidpulverulent material into said upper compartment in counteriiow to saidgas, and gas-pressure-responsive control means sensitive to the pressurediiferential between said compartments and coupled with said valve meansfor maintaining the rate of gas flow at a value adapted to hold saidpulverulent material floatingly suspended above said partition means foran extended period.

6. In a device for heating pulverulent material, in combination, ahousing, substantially horizontal partition means in said housingsubdividing the interior thereof into a lower and an upper compartment,said partition means being formed with at least one passageinterconnecting said compartments, a source of pressure differentialbetween said compartments, means including said source for passing aflow of hot gas upwardly through said passage from said lower to saidupper compartment, adjustable valve means in said passages for changingthe effective cross-sectional area thereof, feed means for continuouslyintroducing a supply of said pulverulent material into said uppercompartment in counterr'iow to said gas, gas-pressure-responsive controlmeans sensitive to the pressure differential between said compartmentsand coupled with said valve means for maintaining the rate of gas fiowat a value adapted to hold said pulverulent material floatinglysuspended above said partition means for an extended period, saidcontrol means being differentially connected with said compartment forvarying said cross-sectional area substantially in step with thepressure drop across said partition means and a layer of said materialfloating thereabove, thereby maintaining the thickness of said layersubstantially constant.

7. In a device for heating pulverulent material, in combination, ahousing, substantially horizontal partition means in said housingsubdividing the interior thereof into a lower and an upper compartment,said partition means being formed with an array of helicoidallyascending passages interconnecting said compartments, a source ofpressure differential between said compartments, means including saidsource for passing a flow of hot gas upwardly through said passages fromsaid lower to said upper compartment, adjustable valve means in saidpassages for changing the effective cross-sectional area thereof, feedmeans for continuously introducing a supply of said pulverulent materialinto said upper compartment in counterflow to said gas,gas-pressure-responsive control means, sensitive to the pressuredifferential between said compartments and coupled with said valve meansfor maintaining the rate of gas flow at a value adapted to hold saidpulverulent material floatingly suspended above said partition means foran extended period, said control means being differentially connectedwith said compartment for varying said cross-sectional areasubstantially in step with the pressure drop across said partition meansand a layer of said material swirling thereabove, thereby maintainingthe thickness of said layer substantially constant.

References Cited in the file of this patent UNITED STATES PATENTS2,078,955 Lipscomb May 4, 1937 2,634,116 \Vitt Apr. 7, 1953 2,668,041Knibbs Feb. 2, 1954 2,785,886 Muller Mar. 19, 1957

1. A DEVICE FOR HEATING PULVERULENT MATERIAL, COMPRISING A HOUSINGFORMING A HEATING CHAMBER, DUCT MEANS FOR INTRODUCING A FLOW OF HOT GASINTO A LOWER PORTION OF SAID CHAMBER, FEED MEANS FOR INTRODUCING ASTREAM OF PULVERULENT MATERIAL INTO AN UPPER PORITON OF SAID CHAMBER INCOUNTERFLOW TO SAID HOT GAS, A PERFORATED COLLECTING PLATE POSITIONEDINTERMEDIATE SAID UPPER AND LOWER PORTIONS FOR INTERCEPTING SAID STREAMOF PULVERULENT MATERIAL AND SAID FLOW OF HOT GAS, AND VALVE MEANSRESPONSIVE TO A PRESSURE DIFFERENTIAL IN SAID CHAMBER ON OPPOSITE SIDESOF SAID PLATE FOR MAINTAINING THE THICKNESS OF A LAYER OF SAID MATERIALDEPOSITED THEREON NEAR A PREDETERMINED VALUE.